1. Field of the Invention
The present invention relates to a radar system having a function for setting a watch alarm region.
2. Prior Art
In recent years, the use of general vessels such as pleasure craft and the like has been spreading. The radar systems for such the pleasure craft have been improved so as to be easily operated by an inexperienced user. In such radar systems, is often provided a function for setting a watch alarm region of a display thereof to automatically generate a collision hazard alarm. That is, upon detection of a target ahead of a vessel, the function automatically detects the appearance of an image (echo) of the target in the watch alarm region to generate, for instance, an audible alarm, so long as the watch alarm region is set, advance, in front of the vessel by the user. In thus, the function warms the user that a target appears in front of his vessel, without requiring constant vigilance to observe the radar display.
Hereinafter, will be described a conventional radar system, referring to FIG. 7. Reference numeral 36 designates a plan position indicator display including a cathoderay tube. Reference numeral 37 designates an outer periphery of a image an area shown by the display 36. Reference numeral 38 designates the center of the image, representing a position of the vessel. Reference numeral 39 is a ship heading marker, showing a direction of a bow. Reference numerals 40a and 40b are straight lines dividing a display screen of the display 36, i.e., electronic cursors (hereinafter called EBL), while 41a and 41b are circular range lines dividing the same, i.e., electronic cursors (hereinafter will be called VRM).
42a and 42b are watch alarm regions divided and specified by the EBL 40a and 40b together with the VRM 41a and 41b. Reference numeral 17 designates a target detected by a radar, and reference numeral 18 is an indication of a watch alarm function.
Reference numeral 43 designates a control panel, in which 44 and 45 are EBL and VRM indicating buttons, respectively, and 46 are shift buttons to move the EBL and VRM. Reference numeral 47 is a set button for a watch alarm region.
The two EBL 40a and EBL 40b are, in general, specified for the right- and left-sides services, respectively, of a watch alarm region desired to be set.
The watch alarm region is set as an enclosed region, of which direction is determined by the EBL 40a for the left side and EBL 40b for the right side, in order from the left to the right, clockwise (or in order from the right to the left, counter clockwise), and of which range is determined by the two VRM 41a and 41b. More concretely, a direction is determined by inputting, to begin with, a position of the EBL 40a, then a position of EBL 40b, whereby a watch alarm region is automatically set.
In the conventional way of setting of a watch alarm region, there is, however, concern that the watch alarm region may be designated in a reverse order contrary to the user's intention. For example if the user mistakenly inputs the EBL 40a and 40b shown in FIG. 7 in reverse, region 42a may be designated although the user, desires to set a watch alarm region in 42b. In such that case, in order to set a watch alarm region that is truly intended to be set by the user, the user needs to reset button 47 for the watch alarm region, after reinputting the positions of the EBL 40a and 40b. This requires the user to always designate a watch alarm region while being, aware of the distinction between the EBL 40a and 40b, thus complicating user input operation.